Inhalative Sedation

The MIRUS system consists of the MIRUS-Controller (MC) – the electronic dosing and control unit, and the MIRUS-Exchanger (ME). Both are connected to each other via a so-called Interface-Line of several pressure lines (among others for gas supply and gas monitoring). The MIRUS-Exchanger consiting of the MIRUS-Refector and the MIRUS-Filter, is positioned on the patient directly between Y-piece and tube. Its most important component is the so-called reflector, its carbon fibre material stores the anaesthetic gas reversibly from the expiration of the patient and releases it again into the next inspiration.This is intended to reduce the consumption of anaesthetic. The function is like a miniaturized circulation system such as anaesthetists know it from anaesthesia ventilators – though without the CO2 eliminating properties of the circulation system.

The MIRUS-Reflector is designed for a maximum lifetime of seven days. After that the Reflector must be exchanged. The display of the MIRUS-Controller shows the remaining time of the Reflector. When the service life has expired, the user is asked by suitable hints on the display to change the Reflector.

The MIRUS-Reflector can also be used for several patients one after another. Contamination of the MIRUS-Reflector by patient’s germs or cross contamination is prevented by the MIRUS-Filter. This must be changed daily or after each patient.

The MIRUS-Controller consists of a gas monitor, a respiratory monitoring system and an agent specfic calibrated vaporizer with a reservoir (250 ml capacity for liquid Isoflurane, Sevoflurane or Desflurane). It performs the vaporization of the liquid anaesthetic in a heated high pressure vaporizer and the electronically clocked application of defined gas portions into the inspiration gas mixture, exclusively during the high flow phase at the start of the inspiration.

Due to the conversion of the liquid anaesthetic to the gas phase in the high pressure vaporizer it is also possible to apply with highest accuracy also gases with boiling points in the range of ambient temperature – such as Desflurane.

In addition, the MIRUS-Controller measures continuously the ventilation parameters such as flow, volumes and ventilation rate and has an integrated gas monitor for monitoring the anaesthetic gas concentration in the breathing gases. By preselection of the desired MAC value the MIRUS control unit thus allows the setting of the desired end-tidal anaesthetic concentration which is kept constant independently from tidal volume fluctuations. This is made possible by the electronic control and regulation of the gas application independently from gas flow, frequency and respiratory volumes which are continuously measured and displayed. This so-called MAC-Pilot keeps the set target MAC constant by measuring the gas concentration in the expiration air at the end of the expiration phase (etVA-MAC, et = end-tidal, VA = volatile anaesthetic), calculates the difference between the measured etVA-MAC and the set target MAC and adds this to the next breath taking into account the reflected gas quantity. This permits changes in ventilating modalities to be assessed and compensated. The MAC-Pilot functions therefore similar to a cruise control on modern cars.

Since the end-expiratory or also the end-tidal concentration can be equated to the alveolar concentration, their measurement allows a continuous but above all also valid and reliable statement on the current depth of sedation (Eger et al. 1965). This also eliminates the need for other measurement of the sedation depth such as for example with the artefact afflicted EEG monitoring. This means that the sedation depth can be largely defined and monitored.

For the rare situation of a power failure the control unit is equippedwith a battery for an emergency operation of ten minutes. Emergency operation is integrated.

For further information: MIRUS